This invention relates to fluorine insolubilizing agents (hereinafter referred to as fluorine insolubilizers) and methods of producing them. It has been a common practice to use a fluorine insolubilizer to insolubilize fluorine in soil or drainage and also in waste gypsum for the purpose of environmental preservation. This invention relates to such fluorine insolubilizers and improvements in their production methods.
Examples of conventionally known fluorine insolubilizer include not only aluminum compounds and calcium compounds of many kinds but also phosphates of various kinds such as sodium phosphate (Na3PO4), disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), calcium hydrogen phosphate dihydrate (CaHPO4.2H2O), hydroxy or hydroxyl apatite (Ca5(PO4)3OH), as disclosed, for example, in Japanese Patent Publications Tokkai 2005-305387, 2006-341196, 2007-216156 and 2010-53266, Journal of the European Ceramic Society 26 (2006) 767-770 and Bunseki Kagaku 34 (1985) 732-735.
These conventional fluorine insolubilizers, however, have problems in that their ability to insolubilize fluorine is not sufficient and especially that they take too long a time for insolubilizing fluorine.